THE ABSENCE OF EXTRACELLULAR CALCIUM POTENTIATES THE KILLING OF CULTURED-HEPATOCYTES BY ALUMINUM MALTOLATE

Dose- and time-dependent killing of cultured rat hepatocytes was produ ced by aluminum maltolate (AlM), a neutral, water-soluble complex of a luminum 3-hydroxy-2-methyl-4H-pyran-4-one. Treatment with 10 mM AlM fo r 1 h killed 50% or more of the cells within 3 h. Removal of calcium f rom the culture medium or treatment with calcium channel blockers (ver apamil, nifedipine, diltiazem) potentiated the cell killing. By contra st, inhibition by thapsigargin of the sequestration of intracellular c alcium by the endoplasmic reticulum reduced the toxicity of AlM. In tu rn, activation of protein kinase C with 12-O-tetradecanoylphorbol 13-a cetate or activation of protein kinase A with 8-[4-chlorophenylthio]ad enosine 3',5'-cyclic monophosphate also reduced the toxicity of AlM. B y contrast, inhibition of protein kinase activity by staurosporine pot entiated the cell, killing. Staurosporine, however, did not reverse th e protection afforded by thapsigargin. Hepatocytes treated with AlM fo r 1 h were rescued by adding deferoxamine as late as 90 min following the removal of AlM, whereas pretreatment for 1 h with deferoxamine did not prevent the toxicity of AlM. ATP depletion did not precede loss o f viability. Pharmacologic probes excluded oxidative stress as a mecha nism of lethal injury by AlM, and inhibition of protein synthesis by c ycloheximide did not protect the hepatocytes, thereby excluding activa tion of a cell death program. These data define a new model in which a luminum kills liver cells by a mechanisms distinct from previously rec ognized pathways of lethal cell injury. It is hypothesized that alumin um binds to cytoskeletal proteins intimately associated with the plasm a membrane. This interaction eventually disrupts the permeability barr ier function of the cell membrane, an event that heralds the death of the hepatocyte. The intracellular calcium ion concentration and protei n phosphorylation may modify the interaction of aluminum with its crit ical targets. Alternatively, aluminum may inhibit the phosphorylation of cytoskeletal elements, thereby interfering with their function. (C) 1995 Academic Press, Inc.